1. Field of the Disclosure
Embodiments disclosed herein relate generally to systems and methods for producing slurries for re-injection at a work site. More specifically, embodiments disclosed herein relate to systems and methods for producing high-density slurries for re-injection at a work site. More specifically still, embodiments disclosed herein relate to systems and methods for producing high-density slurries for re-injection at a work site using a module to convert cutting storage and transfer vessels at the work site.
2. Background
In the drilling of wells, a drill bit is used to dig many thousands of feet into the earth's crust. Oil rigs typically employ a derrick that extends above the well drilling platform. The derrick supports joint after joint of drill pipe connected end-to-end during the drilling operation. As the drill bit is pushed further into the earth, additional pipe joints are added to the ever lengthening “string” or “drill string”. Therefore, the drill string includes a plurality of joints of pipe.
Fluid “drilling mud” is pumped from the well drilling platform, through the drill string, and to a drill bit supported at the lower or distal end of the drill string. The drilling mud lubricates the drill bit and carries away well cuttings generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth's surface. When the drilling mud reaches the platform, it is contaminated with small pieces of shale and rock that are known in the industry as well cuttings or drill cuttings. Once the drill cuttings, drilling mud, and other waste reach the platform, a “shale shaker” is typically used to remove the drilling mud from the drill cuttings so that the drilling mud may be reused. The remaining drill cuttings, waste, and residual drilling mud are then transferred to a holding trough for disposal. In some situations, for example with specific types of drilling mud, the drilling mud may not be reused and it must be disposed. Typically, the non-recycled drilling mud is disposed of separate from the drill cuttings and other waste by transporting the drilling mud via a vessel to a disposal site.
The disposal of the drill cuttings and drilling mud is a complex environmental problem. Drill cuttings contain not only the residual drilling mud product that would contaminate the surrounding environment, but may also contain oil and other waste that is particularly hazardous to the environment, especially when drilling in a marine environment.
In the Gulf of Mexico, for example, there are hundreds of drilling platforms that drill for oil and gas by drilling into the subsea floor. These drilling platforms may be used in places where the depth of the water is many hundreds of feet. In such a marine environment, the water is typically filled with marine life that cannot tolerate the disposal of drill cuttings waste. Therefore, there is a need for a simple, yet workable solution to the problem of disposing of well cuttings, drilling mud, and/or other waste in marine and other fragile environments.
Traditional methods of disposal include dumping, bucket transport, cumbersome conveyor belts, screw conveyors, and washing techniques that require large amounts of water. Adding water creates additional problems of added volume and bulk, pollution, and transport problems. Installing conveyors requires major modification to the rig area and involves extensive installation hours and expense.
Another method of disposal includes returning the drill cuttings, drilling mud, and/or other waste via injection under high pressure into an earth formation. Generally, the injection process involves the preparation of a slurry within surface-based equipment and pumping the slurry into a well that extends relatively deep underground into a receiving stratum or adequate formation. The basic steps in the process include the identification of an appropriate stratum or formation for the injection; preparing an appropriate injection well; formulation of the slurry, which includes considering such factors as weight, solids content, pH, gels, etc.; performing the injection operations, which includes determining and monitoring pump rates such as volume per unit time and pressure; and capping the well.
In some instances, the cuttings, which are still contaminated with some oil, are transported from a drilling rig to an offshore rig or ashore in the form of a thick heavy paste or slurry for injection into an earth formation. Typically the material is put into special skips of about 10 ton capacity that are loaded by crane from the rig onto supply boats. This is a difficult and dangerous operation that may be laborious and expensive.
U.S. Pat. No. 6,709,216 and related patent family members disclose that cuttings may also be conveyed to and stored in an enclosed, transportable vessel, where the vessel may then be transported to a destination, and the drill cuttings may be withdrawn. The transportable storage vessel has a lower conical section structured to achieve mass flow of the mixture in the vessel, and withdrawal of the cuttings includes applying a compressed gas to the cuttings in the vessel. The transportable vessels are designed to fit within a 20 foot ISO container frame. These conical vessels will be referred to herein as ISO vessels.
As described in U.S. Pat. No. 6,709,216 and family, the ISO vessels may be lifted onto a drilling rig by a rig crane and used to store cuttings. The vessels may then be used to transfer the cuttings onto a supply boat, and may also serve as buffer storage while a supply boat is not present. Alternatively, the storage vessels may be lifted off the rig by cranes and transported by a supply boat.
Space on offshore platforms is limited. In addition to the storage and transfer of cuttings, many additional operations take place on a drilling rig, including tank cleaning, slurrification operations, drilling, chemical treatment operations, raw material storage, mud preparation, mud recycle, mud separations, and others.
Due to the limited space, it is common to modularize these operations and to swap out modules when not needed or when space is needed for the equipment. For example, cuttings containers may be offloaded from the rig to make room for modularized equipment used for slurrification. These lifting operations, as mentioned above, are difficult, dangerous, and expensive. Additionally, many of these modularized operations include redundant equipment, such as pumps, valves, and tanks or storage vessels.
Slurrification systems that may be moved onto a rig are typically large modules that are fully self-contained, receiving cuttings from a drilling rig's fluid mud recovery system. For example, PCT Publication No. WO 99/04134 discloses a process module containing a first slurry tank, grinding pumps, a system shale shaker, a second slurry tank, and optionally a holding tank. The module may be lifted by a crane on to an offshore drilling platform.
Slurrification systems may also be disposed in portable units that may be transported from one work site to another. As disclosed in U.S. Pat. No. 5,303,786, a slurrification system may be mounted on a semi-trailer that may be towed between work sites. The system includes, inter alia, multiple tanks, pumps, mills, grinders, agitators, hoppers, and conveyors. As discussed in U.S. Pat. No. 5,303,786, the slurrification system may be moved to a site where a large quantity of material to be treated is available, such as existing or abandoned reserve pits that hold large quantities of cuttings.
U.S. Pat. No. 6,745,856 discloses another transportable slurrification system that is disposed on a transport vehicle. The transport vehicle (i.e., a vessel or boat) is stationed proximate the work site (i.e., offshore platform) and connected to equipment located at the work site while in operation. Deleterious material is transferred from the work site to the transport vehicle, wherein the deleterious material is slurrified. The slurry may be transferred back to the work site for, in one example, re-injection into the formation. Alternatively, the slurry may be transported via the transport vehicle to a disposal site. As disclosed in U.S. Pat. No. 6,745,856, storage vessels are disposed on the transport vehicle for containing the slurry during transportation. While in-transit to the disposal site, agitators disposed in the storage vessels may agitate the slurry to keep the solids suspended in the fluid.
While these systems and methods provide improved processes in slurrification and re-injection systems, they require difficult, dangerous, and expensive lifting and installation operations, as described above. Additionally, these processes may require lengthy installation and processing times that may reduce the overall efficiency of the work site.
During cuttings re-injection operations, a slurry is prepared including a fluid and cleaned drill cuttings. Typically, the slurry is prepared by mixing together drill cuttings previously classified by size at a desired ratio with a fluid, such that a slurry is created that contains a desirable percentage of drill cuttings to total volume. Those of ordinary skill in the art will appreciate that generally, the solids content of slurries used in cuttings re-injection operations is about 20 percent solids content by volume. Thus, in a given cuttings re-injection operation, a slurry is prepared for re-injection by mixing drill cuttings with a fluid until the solids content of the slurry is 20 percent. After preparation of the slurry, the slurry is pumped to a vessel for storage, until a high-pressure injection pump is actuated, and the slurry is pumped from the storage vessel into the wellbore.
In operations attempting to increase the solids content of the slurry to greater than 20 percent, thereby allowing for the re-injection of more cuttings into a formation, such operations have resulted in inconsistent, and thus, ineffective slurries. Typically, when a drilling operator has attempted to increase the solids content of the slurry, the slurry with a solids content of greater than 20 percent is created by mixing drill cuttings with a fluid, and then storing the mixture as described above. Because slurries are typically made in batches, stored, and then injected into the wellbore, during the storage of the slurry, prior to re-injection, the solids in the slurry would fall out of the suspension. As the solids fall out of the suspension, they may block or otherwise clog injection equipment, including flow lines and pumps, thereby preventing the slurry from being re-injection.
Furthermore, even if the slurry of greater than 20 percent solids content was injected into the wellbore, because the slurry is typically injected in batches, significant time may exist between injection operations. Thus, a slurry with a greater than 20 percent solids content may be injected downhole and the solids may begin to fall out of the suspension downhole during re-injection downtime. If the solids fall out of the suspension in the wellbore, prior to reaching the targeted formation, the solids may solidify in the wellbore, thereby blocking the wellbore for subsequent re-injection. Wellbores blocked in this way must then either be re-drilled, the cuttings removed using costly operations, or abandoned. Because of the high costs associated with removing cuttings from a blocked wellbore, wells blocked during re-injection are often abandoned, thereby causing a drilling operator to process residual slurry and cuttings using alternate methods.
Examples of alternate methods may include disposal of the cuttings in on-land cuttings pits or transferring the cuttings to alternate re-injection sites. In either situation, the drilling operation may incur additional expenses associated with the transport of the cuttings and slurry to alternate disposal sites, thereby increasing the overall cost of the drilling operation.
Thus, there exists a continuing need for slurrification systems that may increase the solids content of a re-injection slurry and provide a modular solution for cuttings re-injection operations.